Method of and apparatus for the development of light sensitive diazotype materials



Sept. 8, 1964 J. G. B. HALDEN 3,147,637

METHOD OF AND APPARATUS FOR THE DEVELOPMENT OF LIGHT SENSITIVE DIAZOTYPEMATERIALS Filed Oct. 5, 1961 3 Sheets-Sheet l 39 ELECTRONIC mvmg {fsrecov ,CONTROL mm 71 if f IRIVE AMMONIA INTERVAL MOTOR PUH TIMER 1 I ,4 47HEATER FIG].

ELECTRONIC mvms SPEED [j comm "e a 32 I 7/ 70 um: AMMONIA T MOTOR PUMPmennosm HEATER ANHYDROUS AMMONIA CONTROL 4o ELisgERgNlfi DRIVING P cm 2I 7' 7/ 76 omve wmn MOTOR PUMP 27 I4 i ,J- "l I THERMOSTAT EATER HGJ.

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Sept. 8, 1964 J G. B. HALDEN 3,147,687

METHOD OF AND APPARATUS FOR THE DEVELOPMENT OF LIGHT SENSITIVE DIAZOTYPEMATERIALS Filed Oct. 5, 1961 3 Sheets-Sheet 2 Sept. 8, 1964 J. G. B.HALDEN 3,147,687

METHOD OF AND APPARATUS FOR THE DEVELOPMENT OF LIGHT SENSITIVEDIAZOTYPEMATERIALS Filed Oct. 5, 1961 3 Sheets-Sheet 5 T Q I o I FDjf'G9 I 44 47 U 49 43 I 45 I 40 42 l 38 4a I b '53 J9 52 I 5: fi l---- F: 34sl/prL FIG.6.

United States. Patent METHOD OF AND APPARATUS FOR THE DEVEL- OPMENT OFLIGHT SENSITIVE DIAZOTYPE MATERIALS Joseph Gerald Broctou Halden, LenhamHeath, near Maidstone, Kent, England, assignor to Ozalid CompanyLimited, Loughton, England, a British company Filed Oct. 5, 1961, Ser.No. 143,248 Claims. (CI. 95-94) In the development of light sensitivediazotype materialsby means of ammonia gas it is known that for optimumdeveloping conditions a certain proportion of water vapour must bepresent with the ammonia gas in the development atmosphere. Thedevelopment atmosphere is normally produced by heating an aqueoussolution of ammonia in a vaporizing device disposed either within thedeveloping chamber or externally thereof, the spent solution beingdrained away to waste after it has been heated to liberate ammonia gasand water vapour.

Unless the development atmosphere contains a certain minimum proportionof water vapour satisfactory development cannot be achieved while if thewater vapour content of the development atmosphere is excessive, thereis a tendency for water vapour to condense on and soil the diazotypematerial undergoing development and also to retard the process ofdevelopment by excessive dilution of the ammonia gas.

In existing developing machines no provision is made for varying theenergy input to the heater. Even if there is no provision for varyingthe speed of throughput of the exposed diazotype material it isnecessary from time to time to vary the rate of supply of ammoniasolution to the vaporizing device with the result that there is acorresponding and undesirable variation in the relative proportions ofwater vapour and ammonia gas in the development atmosphere. velopingmachine provide, however, for variation in operating rate, i.e. in speedof operation of the motor which feeds the diazotype material through themachine, and it is known to arrange for the rate of supply of ammoniasolution to the vaporizing device to be varied automatical- 1y to suitchanges in setting of the speed control of the machine. In such machinesthe heater is set to operate at conditions appropriate for maximumsetting of the speed control. In practice, however, development machinesare operated more often than not at speeds below the maximum. As theresult they operate inefficiently because the development atmospherecontains an excessive proportion of Water vapour and this reduces theefiiciency of-development and may, as already noted, result in soilingof the diazotype material.

The present invention provides a method of developing light sensitivediazotype material which comprises supplying at a controlled rate to avaporizing zone fluid which, when heated, will produce a developingvapour consisting of a mixture of ammonia gas and water vapour andsupplying heat to said fluid in the vaporizing zone at a ratecorresponding to the rate of supply thereto of the fluid so as tomaintain in the vaporizing zone a predetermined control temperature andthereby maintain substantially constant at a predetermined value therela-. tive proportions of ammonia gas and water vapour in thedeveloping atmosphere.

The fluid supplied to the vaporizing zone may be an aqueous solution ofammonia, in which case it is preferred to use the commercially availablesolution of specific gravity 0.910. As an alternative, however,anhydrous ammonia and water may be separately supplied to the vaporizingzone. Where the developing apparatus includes provision for varying therate of feed of exposed diazoztype material through a developing zone,we may Most modern forms of de- Patented Sept. 8, 1$64 arrange for thefeed of ammonia solution, or of anhydrous ammonia and water, to thevaporizing zone (which may be located in the developing chamber orexternally thereof) to be controlled automatically in accordance withchanges in the rate of feed of diazotype material.

The control of heat input to the vaporizing zone may be efiected by athermostat sensitive to the temperature of the liquid in the vaporizingzone or by an interval timer which is controlled by the mechanism forvarying the speed of operation of the machine. By appropriate adjustmentof the thermostat or interval timer it is possible to vary as desiredthe control temperature and therefore the relative proportions ofammonia gas and water vapour in the development atmosphere.

In existing developing machines, the spent liquid from the vaporizingzone is drained to the bottom of the developing chamber where itstemperature drops, with the result that the spent liquid absorbs ammoniagas from the development atmosphere. According to a feature of theinvention this tendency is reduced to a minimum by separating spentliquid leaving the vaporizing zone from the vapour phase at atemperature approximating to the control temperature. The spent liquidthen has a minimum content of ammonia gas.

In existing developing machines, the relative PI'OPOI! tions by weightof ammonia gas and water vapour are of the order of 30% to 70%. Byoperating a developing machine in accordance with the above-describedmethed it is possible to work with a developing atmosphere containing apreponderating amount of ammonia gas, e.g. an atmosphere containing -75%by weight of ammonia gas and 40-25% by weight of water vapour.

It has been found in practice that optimum developing conditions areprovided if water vapour is evolved to the extent of between 15% minimumand 30% maximum of the water present in an aqueous ammonia solution ofspecific gravity .910. An aqueous ammonia solution of specific gravity.910 consists of 25.25% ammonia and 74.75% water by weight therefore theevolution of, for example, 20% of the total available water vapour and90% of the total ammonia results in a concentrated developing mixture,consisting of 64% ammonia gas and 36% water vapour. This mixtureprovides very much more efiicient development than is possible by meansof the proportions of ammonia gas and water vapour vaporized underconventional methods and utilizing conventional apparatus.

The following experimental results, in which the control temperature inthe vaporizing zone was determined by a sensitive thermostat, illustratethe variations obtained in the proportions of ammonia gas and Watervapour in the developing atmosphere under dillerent temperatureconditions and also illustrate the desirability of utilizingcontrollable temperature conditions.

Experimental Results With External Vaporizer Iercent- Percentageconcenage of Percenttration in develop- F. control SG of water age ofing atmosphere temp. efliluent vaporammonia ized extracted The productsof the vaporizer were fed to the developing zone. Poor results wereobtained from serial (a).

atmosphere was in the region of 65% to 35%. Less water resulted inconditions too dry to permit complete coupling, more water reduced theconcentraion of NH and slowed down coupling and also induced undesirablechanges in the hue of some black line coatings.

By varying the control temperature the proportions of water vapour toammonia gas in the developing atmosphere can be varied at will over avery wide range from about 25% ammonia gas to 75% water vapour to about85% ammonia gas to 15% water vapour from a .910 specific gravity aqueousammonia solution.

Thus suficient heat may be provided fully to vaporize the aqueousammonia solution or the heat input may be reduced to a level at whichvery little water vapour is evolved. 7

It has been found experimentally however that, with a specific design ofmachine, if less than 13% of the water content of a .910 specificgravity aqueous ammonia solution is vaporized performance is badlyaffected and in practice therefore the level of water vaporizationshould not be allowed to fall below 15%. Optimum results with mostmaterials are obtained at a vaporization level of about 20% whichprovides a developing atmosphere of 64% ammonia gas to 36% water vapour.

The following experimental results show in tabulated form the elfect ofutilizing an interval timer to control the vaporization of aqueousammonia solution in a specific developer unit. The higher proportion ofwater vapour to NH at a given level of effluent S6 in this case isbecause the vaporizer was fitted internally. In the case of theexperimental results quoted previously for the external vaporizer,condensation occurred in the connecting tube between the vaporizer andthe developing chamber and in the distribution tube, resulting in alower However, it will be appreciated that there will be a time lagbetween the selection of the desired proportions of ammonia gas to watervapour and the stabilisation of the developing atmosphere at theseselected 'proportions. This has been established experimentally atapproximately 10 to 15 minutes when the machine is in operation.

Particularly when thermostatically controlled means are employed,legible developed copies may be obtained extremely quickly, within 3 to4 minutes of switch on even though the developing chamber is still cold.This is due to the fact that because the amount of water vaporized islimited and the proportion of, ammonia gas in the mixture much greater,recombination of ammonia with the water when discharged into the colddeveloping chamber is not sufiicient to prevent partial development ofmaterials taking place under these conditions. Thus by the time theprinting lamp of the machine has warmed up legible developed copies canbe produced.

However, whether an interval timer or whether a thermostat is employedthe optimum control temperature or interval timer setting may be easilyobtained by reference to the specific gravity of the spent liquid fromwhich can be calculated, in conjunction with the measured volume of theeffluent, the proportions of ammonia gas and Water vaporization obtainedfor given settings.

It has been found experimentally that the embodiment of the inventionemploying thermostatic control is capable of maintaining the developingconditions in a machine contsant within very close limits in respect ofproportions of ammonia gas and Water vapour and it has also been foundthat provided these proportions are maintained at the optimum level theoperating temperature of the developing tank can be substantiallyreduced proportion of water vapour in the developing atmosphere. 35without significantly aife'cting the developing performance ExperimentalResults With Internal Vaporizer With Asbestos Lagged Tube.

Heater Controlled by Interval Timer Percent- Percent- Percentage concen-Nominal Watts Feed age of age of tration of develop- Interval tlmersetting, energy, per ml. rate, SG effluwater ammonia ing atmospherepercent watts ml. lmin. ent vaptzirextracted ize These experiments wereconducted to establish the eifect of higher water vaporization rates onvarious diazo coatings. The results confirmed the earlier findings thatnothing is gained by vaporizing more than 20% to 25 of the water contentof a .910 liquor.

It will be noted that the control of the system is good and thatvaporizer performance remains nearly constant in relation to the SG ofthe efiluent at widely differing feed rates and heat inputs even withthe relatively unrefined controlby an interval timer.

With a correctly designed vaporizer system controlled by a sensitivethermostat, however, an extremely'accurate control can be imposed andthe performance of the developing machine can be stabilised at anydesired leve within the range of the system. V

Means may be provided to permit the machine operator to select at willapproximately correct operating pro portions to suit the specificrequirements of different types of diazo materials and in thisconnection it will be'appreci'ated that in the case of some lacquercoated materials it may be necessary to soften the lacquer surface topermit adequate penetration of ammonia gas thereto and consequently ahigh watervaporizati'on rate may be desirable.

of the unit. This is particularly advantageous when developing solventcoated materials particularly those with thermoplastic bases.

The invention includes apparatus for developing light sensitivediazotype materials comprising a developing chamber, means for feedingexposed diazotype material through a developing zone in the chamber, avaporizer, means for supplying to the vaporizer at a variable rate fluidadapted when heated to produce a developing atmosphere constituted by amixture of ammonia gas and water vapour for conveyance to the developingzone, and means for supplying heat to the vaporizer at a rate controlledautomatically by the rate of supply thereto of said fluid so as tomaintain a predetermined control temperature in the vaporizer andtherefore substantially constant relative proportions of ammonia gas andwater vapour in the developing atmosphere.

The rate of feed of aqueous ammonia solution can be automatically variedin direct proportion to the rate of feed of diazotype material throughthe machine in various ways. Thus in pump fed machines, in which themotor driving the diazotype material feeding means has an electronicspeed control unit fitted with a potentiometer for adjusting it, thecontrol shaft of the poten- I tiometer may be mechanically coupled tothe ammonia solution pump so as to vary the stroke of the pump.Alternatively, the ammonia pump may be operated direct by a suitable camarrangement from one of the rollers of the machine which varies thenumber of strokes in a given time period according to the speed of themachine. In gravity fed machines where a drip controlled gravity fedsystem is used variation in the ammonia feed may be achievedautomatically by mechanical or electrical operation of the drip controlin accordance with the machine speed.

In order to utilize the products of vaporization to the best advantageit is necessary to ensure complete mixing of ammonia gas and watervapour and even distribution throughout the developing chamber and forthis purpose recourse may be had to the apparatus described below.

It has been found in practice that the apparatus of the presentinvention will permit the speed of processing to be at least doubled fora given exposing surface and will provide completely even conditionsacross the full width of the machine, will improve the developed colour,particularly of blackline diazo materials, will eliminate condensationmarking of prints, and will eliminate or at least very substantiallyreduce paper curl in processing due to moisture absorption. Further,since the working temperature of the developing chamber can besubstantially reduced the tendency for lacquered materials to stickwhile traversing the developing zone is very substantially reduced ifnot completely eliminated.

These alternative forms of developing apparatus according to theinvention will now be described in more detail, by way of example, withreference to the accompanying drawings in which FIGS. 1-3 are blockdiagrams illustrative of the three forms of developing apparatus,

FIG. 4 is a section through the developing chamber utilized inaccordance with FIG. 1, but showing in chaindotted lines certainmodifications required for compliance with FIGS. 2 and 3 respectively,

FIG. 5 is a section on the line V-V in FIG. 4, and

FIG. 6 is a sectional view of control apparatus complying with FIG. 1.

Like reference numerals indicate like'parts throughout the figures.

The system shown in block diagram form in FIG. 1 will first bedescribed. The developing chamber 1 shown in FIGS. 4 and 5 has end walls2, 3, a bottom wall 4, an upper perforated Wall 5, and side walls, oneof which is shown at 6.

The upper perforated wall 5 of the developing chamber is sealed by anendless moving belt or blanket (not shown) which traverses the materialto be developed over the perforated wall 5 and prevents the developingvapours emanating through the perforations escaping into the surroundingatmosphere. The diazotype material is traversed through the machine inknown manner by a variable speed electric motor 79 (FIG. 1) having anelectronic speed control 71 provided with a speed control shaft 39.

The developing chamber 1 contains a vaporizer including a trough 7,extending across the width of the developing chamber. The trough 7 isinsulated by means of asbestos or like lagging 8 (FIG. 5).

The trough 7 extends into the chamber 1 through an aperture 10 providedfor the purpose in the end Wall 2 and an end plate 11 and sealing washer12 are provided to prevent escape of vapour from the chamber at thispoint.

The trough 7 slopes downwardly from the wall 2 towards the wall 3 topermit the aqueous ammonia solution fed to the interior of the trough 7to flow down it from one end to the other. Aqueous ammonia solution isfed to the interior of the trough 7 as later described through a feedpipe 13.

Inside the trough 7 is an electric heating element 14 for heating theaqueous ammonia solution as it flows down the trough 7.

As the aqueous ammonia solution is heated it vaporizes to evolve ammoniagas and water vapour, the spent solution draining to form a pool 15 atthe lower end of the trough 7. As this spent liquid is maintained at thetemperature at which the vapours were evolved no recom bination ofammonia gas with it will take place.

To remove this spent solution from contact with the evolved vapour atthe prevailing control temperature a port 16 is provided in the end wall17 of the trough 7, and the spent solution is conveyed to the exteriorof the developing chamber 1 by a pipe 18 which extends through sealingwashers 19 and an end plate 26) provided externally of the wall 3 of thedeveloper chamber.

Any water vapour which may condense on the inner walls of the developingchamber 1 is drained through a port 21, a pipe 22 and a vapour trap 23.

The trap 23 consists of a container 24 secured to the bottom Wall 4 ofthe developing chamber and into which the pipe 21 extends downwardlythereinto to within a short distance of its bottom wall 25. Near theupper end of the container 24 is an overflow pipe 26 leading to a wastecontainer (not shown). The pipe 18 which removes the spent solution fromthe trough 7 is connected to the trap 23 near its lower wall 25.

The trap 23 operates as a constant level device andv effectivelyprevents any recombination of ammonia gas with the water contained inthe waste so that optimum conditions prevail within the developingchamber 1.

Assuming that ammonia solution of SG .910 is supplied to the vaporizerthrough the feed pipe 13, the hot eflluent discharged from the vaporizermaintains the liquid in the trap 23 at a temperature approximating tothe control temperature and a SG of .989 to .990. The small amount ofcondensate which drains into the trap 23 through the tube 22 is raisedin the trap to a temperature such that nearly all the ammonia which hasbeen reabsorbed in the condensate is again driven off into thedeveloping chamber. Virtually all loss of ammonia into the effluent isthus prevented and about 93% of the available ammonia is extracted undernormal operating conditions. Known developing machines require a largenumber of heaters to prevent condensation in the developing chamber. Theapparatus of the present invention can be operated effectively with onlyone such heater, which is not shown in the drawings, to maintain theambient temperature of the developing chamber at a level sufficient topromote rapid development.

The vaporizing tray is divided by a wall 28 into tw compartments 29, 30communicating via a central aperture 31 in the wall 28. The developingatmosphere escapes from the compartment 30 of the vaporizer to thedeveloping zone through holes 9. There is thus provided a system ofbattles which causes the evolved ammonia gas and water vapour to bebrought to a single point 31 for mixing and then distributes the mixturethrough the holes 9 across the width of the developing chamber.

Referring now to FIG. 6 of the drawings aqueous ammonia solution from apipe line 33 leading from a source of supply (not shown) is pumped bymeans of a bellows pump 32 of known construction to the pipe line 13which leads to the vaporizer trough 7.

The pump 32 is operated by means of a cam 36, driven from a constantspeed drive motor 80 (FIG. 1), through a follower 37 carried by a lever34, pivoted at 35 to a sleeve 38 and pivoted at 72 to an arm '73. Thearm 73 is loaded by a spring 74, mounted to rock on a fixed pivot andconnected to the pump 32 by a stirrup 76.

The main speed control shaft 39 serves, when rotated, to adjust thepotentiometer 40 of the electronic speed control 71 (FIG. 1). Rotationof the shaft 39 to adjust the rate at which diazotype material is fedthrough the machine effects longitudinal adjustment on the shaft of thesleeve 38, which is threaded to the shaft, and so shifts the position ofthe pivot 35 and effects a corresponding adjustment of the stroke of thepump 32 and therefore of the rate of supply of ammonia solution to thevaporizer.

An independent manual adjustment of the rate of supply of ammoniasolution is aiforded by a shaft 41, which carries a threaded sleeve 77formed with a knife edge 78. Adjustment of this knife edge serves tovary the stroke which is imparted to the pump 32 by the cam 36.

The heat input to the heater 14 (FIG. 4) is controlled by an intervaltimer 42 rotatably mounted on a bracket 43 and provided with anoperating spindle 44. This interval timer is of known type, thus it maybe of the type sold by Sunvic Controls Ltd. under the trademarkSimmerstat. It comprises a pair of contacts which control the supply ofcurrent from the mains to the heater 14, and includes a bimetal stripwhich is adjustable by a cam and an associated heater element. Thecontacts are normally closed so that when connected to an electricalsupply current will flow through the heater element around the bimetalstrip. According to the setting of the cam a greater or lesser amount ofheat will be required to cause the bimetal strip to bend sufiiciently tocause the contacts to open and break the flow of current to the heater14 of the vaporizer. The cam is rotated by the operating spindle 44 andthus any relative movement of the spindle 44 and the body 45 of theinterval timer will alter the time intervals during which the electricalload (in this case the heater 14) is switched on or off. The rate ofsupply of heat to the vaporizer can thus be adjusted both byrotation ofthe spindle 44 and by rotation of the body 45 of the interval timer 42.

The spindle 44 carries a sprocket 47 connected by a chain 49 to asprocket 48 secured to the speed control spindle 39. Accordingly as thespindle 39 is rotated to increase or decrease the speed of operation ofthe machine, the spindle 44 will be rotated to effect correspondingadjustment through the interval timer 42 of the output of the heater 14.

The shaft 41 for manual regulation of the rate of feed of aqueousammonia solution carries a sprocket 50 meshing with a second sprocket 51which is mounted on a stub axle 52. The stub axle 52 carries a secondsprocket 53 conected by a chain 55 to a sprocket 54 rotatably mounted onthe spindle 44 and fixed to the mounting sleeve 43A of the intervaltimer which is free to rotate in relation to the bracket 43.

Accordingly as the ammonia feed rate control shaft 41 is rotated thebody 45 of the interval timer is rotated to adjust the energy input tothe heater 14.

As an alternative to the use of an interval timer for varying the heatinput to the vaporizer, a thermostat 27 may be provided in the vaporizeras shown in chain dotted lines in FIG. 4. The ammonia solution pump 32is adjusted to deliver ammonia at a rate proportionate to the speed ofthe motor 70 and also has an independent manual adjustment as shown inFIG. 6. This system is shown in block diagram form in FIG. 2. Thethermostat 27, which is adjustable to maintain a desired predeterminedcontrol temperature in the vaporizer cuts out the heater 14 whenever thepreset control temperature is reached and cuts the heater in again assoon as the temperature in the vaporizer tends to fall below the presetvalue. The thermostat responds to any change in the rate of supply ofammonia solution to the vaporizer or to any fluctuation of theelectrical supply voltage or to any change in the specific gravity ofthe ammonia solution used, to adjust the energy input to the heater insuch fashion as to maintain the control temperature at the preset value.The control imposed by thethermostat is therefore very much more precisethan that provided by an interval timer and compensates fully for anychange in operating conditions which can occur except a change of thespecific gravity of the ammonia solution. In this case since there willbe a change in the proportions of ammonia and water in the solutionsupplied to the vaporizer and the amount of ammonia vaporized willincrease or decrease according to whether the solution supplied isstronger or weaker. The quantity of water vaporized, however, willremain constant as will the specific gravity of the effluent since theseare dictated by the control temperature. a

It is in the automatic compensation for uncontrollable variations of oneor more of the factors that therm ostatic control is much superior tointerval timer control, since the latter is unable to compensate forvariation of these factors, which will thus cause deviations from thedesired performance.

A thermostat of high sensitivity is required and one responsive to atemperature change of less than 1 Fahrenheit has been found verysuitable for the purpose. A commercial type thermostat of lowsensitivity will not provide satisfactory results. a p

In the arrangement shown schematically in FIG, 3, the pump 32 serves topump water only to the vaporizer, anhydrous ammonia being supplied tothe vaporizer from a cylinder through a pipe 46A, shown in chain dottedlines in FIG. 4. The control temperature is maintained by a thermostat27 as in FIG. 2, and the stroke of the pump 32 is adjusted as describedwith reference to FIG. 6. Adjustment of the speed control shaft 39effects a corresponding adjustment of a valve 46 (FIG. 4) forcontrolling the admission of anhydrous ammonia to the vaporizer and ofthe pump 32 for controlling the supply of water. I

Adjustment of the manual control shaft 41 serves only to adjust thevalve 46 to alter the supply of anhydrous ammonia.

What I claim as my invention and desire to secure by Letters Patent is:v

1. Apparatus for developing light-sensitive diazotype materialcomprising a developing chamber, variable speed means for feedingexposed diazotype material through a developing zone in the chamber,avaporizer, a speed controlling member for adjusting said variable speedmeans, a variable delivery pump adjustable by said speed control meansfor feeding aqueous ammonia to the vaporizer at a rate corresponding tothe rate of feed of material, an electrical heater in the vaporizer forvaporizing said aqueous ammonia to produce a developing atmosphere ofammonia gas and water vapour for conveyance to said developing zone, andmeans responsive to variations in the delivery of said pump for varyingthe input of current to said heater to maintain a predetermined controltemperature inthe vaporizer and thereby controlling the evaporation bothof ammonia gas and of water vapour from said vaporizer to maintainsubstantially constant relative proportions of ammonia gas and watervapour in the developing atmosphere.

2. Apparatus as claimed in claim 1, comprising a pivotedlever connectedto said pump, a cam operative on said lever to cause it to oscillateabout its pivot to actuate the pump and means operable by the speedcontrol member for adjusting the position of the pivot of said lever andthereby varying the delivery of the pump.

3. Apparatus as claimed in claim 2, which includes a stop fordetermining the amplitude of oscillation of said lever and manualcontrol means for adjusting the position of the stop.

4. Apparatus for developing light-sensitive diazotype materialcomprising a developing chamber, variable speed means for feedingexposed diazotype material through a developing zone in the chamber, avaporizer, a speed controlling member for adjusting said variable speedmeans, a variable delivery pump adjustable by said speed control meansfor feeding aqueous ammonia to the vaporizer at a rate corresponding tothe rate of feed of said material, an electrical heater in the vaporizerfor vaporizing said aqueous ammonia to produce a developing atmosphereof ammonia gas and water vapour for conveyance to said developing zone,and an interval timer for intermittently supplying current to saidheater which is adjustable by said speed controlling member to maintaina predetermined control temperature in said vaporizer.

5. Apparatus as claimed in claim 4, which includes a manual control foreifecting simultaneous adjustment of the delivery of said pump and ofsaid interval timer.

6. A method of developing light sensitive diazotype material whichcomprises feeding exposed diazotype material through a developing zone,supplying to a vaporizing zone, from which a developing atmosphere ofammonia gas and water vapor is supplied to the developing zone, anaqueous solution of ammonia at arate controlled automatically by therate of feed of the diazotype material, varying the supply of heat tothe vaporizing zone in accordance with variations in the rate of thesupply of the ammonia solution to said zone so as to maintain in thevaporizing zone a predetermined control temperature and thereby maintainsubstantially constant at a predetermined value the relative proportionsof ammonia gas and Water in the developing atmosphere, and separatingspent liquid leaving the vaporizing zone from the vapor phase at atemperature approximating to the control temperature.

7. Apparatus for developing light-sensitive diazotype materialcomprising a developing chamber, variable speed means for feedingexposed diazotype material through a developing zone in the chamber, avaporizer, means for supplying to the vaporizer, at a rate dependentupon the rate of feed of said material, fluid adapted when heated toproduce a developing atmosphere constituted by a mixture of ammonia gasand water vapor for conveyance to said developing zone, an electricalheater in the vaporizer and means responsive to variations in the rateof supply of fluid to the vaporizer for maintaining substantiallyconstant relative proportions of ammonia gas and water vapor in thedeveloping atmosphere by varying the input of heat to said heater tomaintain a predetermined control temperature in the vaporizer andthereby control the evaporation both of ammonia gas and of water vaporfrom said vaporizer, said responsive means being a thermostat forcontrolling the input of current to said heater to maintain apredetermined control temperature in the vaporizer irrespective ofvariation in the rate of supply of fluid to the vaporizer.

8. Apparatus as claimed in claim 7, wherein said vaporizer includes adownwardly sloping tray wherein said heater is positioned, saidapparatus including a pipe for discharging aqueous ammonia from saidfluid supplying means into the upper end of said tray.

9. Apparatus as claimed in claim 7, wherein said vaporizer includes adownwardly sloping tray wherein said heater is positioned, saidapparatus including pipes for discharging anhydrous ammonia and waterfrom said fluid supplying means into the upper end of said tray.

10. Apparatus for developing light-sensitive diazotype materialcomprising a developing chamber, variable speed means for feedingexposed diazotype material through a developing zone in the chamber, avaporizer, a speed controlling member for adjusting said variable speedmeans, a variable delivery pump adjustable by said speed control meansfor feeding aqueous ammonia to the vaporizer at a rate corresponding tothe rate of feed of said material, an electrical heater in the vaporizerfor vaporizing said aqueous ammonia to produce a developing atmosphereof ammonia gas and water vapor for conveyance to said developing zone,and means responsive to variations in the rate of supply of fluid to thevaporizer for maintaining substantially constant relative proportions ofammonia gas and water vapor in the developing atmosphere by varying theinput of heat to said heater to maintain a predetermined controltemperature in the vaporizer and thereby control the evaporation both ofammonia gas and of water vapor from said vaporizer, said responsivemeans being a thermostat for controlling the input of current to saidheater to maintain a predetermined control temperature in the vaporizerirrespective of variation in the rate of supply of fluid to thevaporizer.

References Cited in the file of this patent UNITED STATES PATENTS2,096,015 Von Meister et al Oct. 19, 1937 2,475,809 Sullivan et al July12, 1949 2,630,744 Wilde Mar. 10, 1953 2,696,771 Frantz Dec. 14, 19542,926,592 Wilde Mar. 1, 1960 FOREIGN PATENTS 664,373 Germany Aug. 25,1938

7. APPARATUS FOR DEVELOPING LIGHT-SENSITIVE DIAZOTYPE MATERIALCOMPRISING A DEVELOPING CHAMBER, VARIABLE SPEED MEANS FOR FEEDINGEXPOSED DIAZOTYPE MATERIAL THROUGH A DEVELOPING ZONE IN THE CHAMBER, AVAPORIZER, MEANS FOR SUPPLYING TO THE VAPORIZER, AT A RATE DEPENDENTUPON THE RATE OF FEED OF SAID MATERIAL, FLUID ADAPTED WHEN HEATED TOPRODUCE A DEVELOPING ATMOSPHERE CONSTITUTED BY A MIXTURE OF AMMONIA GASAND WATER VAPOR FOR CONVEYANCE TO SAID DEVELOPING ZONE, AN ELECTRICALHEATER IN THE VAPORIZER AND MEANS RESPONSIVE TO VARIATIONS IN THE RATEOF SUPPLY OF FLUID TO THE VAPORIZER FOR MAINTAINING SUBSTANTIALLYCONSTANT RELATIVE PROPORTIONS OF AMMONIA GAS AND WATER VAPOR IN THEDEVELOPING ATMOSPHERE BY VARYING THE INPUT OF HEAT TO SAID HEATER TOMAINTAIN A PREDETERMINED CONTROL TEMPERATURE IN THE VAPORIZER ANDTHEREBY CONTROL THE EVAPORATION BOTH OF AMMONIA GAS AND OF WATER VAPORFROM SAID VAPORIZER, SAID RESPONSIVE MEANS BEING A THERMOSTAT FORCONTROLLING THE INPUT OF CURRENT TO SAID HEATER TO MAINTAIN APREDETERMINED CONTROL TEMPERATURE IN THE VAPORIZER IRRESPECTIVE OFVARIATION IN THE RATE OF SUPPLY OF FLUID TO THE VAPORIZER.